Reactive agent and process for decomposing fluorine compounds and use thereof

ABSTRACT

A reactive agent for decomposing fluorine compounds comprising alumina and an alkaline earth metal compound; a process for decomposing fluorine compounds, comprising contacting the reactive agent with a fluorine compound at a temperature of 200° C. or more; and a process for manufacturing a semiconductor device, comprising an etching or cleaning and a decomposing using the reactive agent.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is an application filed under 35 U.S.C. §111(a)claiming benefit pursuant to 35 U.S.C. §119(e)(1) of the filing date ofthe Provisional Application No. 60/156,871 filed Sep. 30, 1999 pursuantto 35 U.S.C. §111(b).

FIELD OF THE INVENTION

The present invention relates to a reactive agent and a process fordecomposing and detoxifying various fluorine compounds such aschlorofluorocarbons (hereinafter simply referred to as “CFC”),hydrochlorofluorocarbons (hereinafter simply referred to as “HCFC”),perfluorocarbons (hereinafter simply referred to as “PFC”),hydrofluoro-carbons (hereinafter simply referred to as “HFC”),perfluoroethers (hereinafter simply referred to as “PFE”),hydrofluoroethers (hereinafter simply referred to as “HFE”) and sulfurfluoride, simultaneously with the compounds produced on using thesefluorine compounds, for example, in an etching or cleaning step duringthe process of manufacturing a semiconductor device, such as HF, SiF₄ orCOF₂.

BACKGROUND OF THE INVENTION

Most of the above-described fluorine compounds are generally stable andharmless to the human body, therefore, their use is outspread in variousfields. In recent years, the amount of HFC as a refrigerant of car airconditioner or the like and PFC for etching or as a cleaning gas in theprocess of manufacturing semiconductors is particularly increased.Furthermore, a large amount of sulfur hexafluoride is being used forcapacitors, transformers and the like because of its excellentelectrical insulating property. These fluorine compounds are a stablecompound and in turn have a large global warming potential coefficient.If such a fluorine compound is released as it is into the globalenvironment, there is a fear that its effect continues for a long periodof time. In particular, SF₆, CF₄, C₂F₆ and the like are a very stablegas and have a very long life in air. Therefore, on discharge aftertheir use, these gases must be released after decomposition into aharmless substance having no effect on the global environment. As analternate compound therefor, PFE and HFE are proposed but these alsohave the same global warming problem. Furthermore, the gas dischargedafter use in the process of manufacturing semiconductor devices containsgases such as HF, SiF₄ and COF₂ and these gases must also be releasedafter decomposition into a safe substance together with theabove-described compounds.

CFC heretofore used in a large amount as a refrigerant, detergent or thelike, and HCFC as an alternate compound thereof cannot be released as itis and must be decomposed into a harmless substance because ozone layerdestruction occurs as a serious environmental problem.

Conventionally, as a technique for decomposing such fluorine compounds,for example, (1) a combustion decomposition method of treating thecompound together with a fuel (see, WO94/05399), (2) a thermaldecomposition method using a reactive agent such as silica or zeolite(see, JP-A-7-116466 (the term “JP-A” as used herein means an “unexaminedpublished Japanese patent application”)), and (3) a catalyticdecomposition method using an alumina or the like (see, JP-A-10-286434)are known.

However, method (1) is disadvantageous in that generation of NO_(x) mustbe controlled during the combustion or a large amount of diluting gas isnecessary, causing a decrease in the decomposing ratio, and moreover, asecondary treatment of HF contained in the exhaust gas after thedecomposition is necessary. Method (2) also has a problem in that a hightemperature of 1,000° C. or more is necessary particularly fordecomposing PFC (e.g., CF₄, C₂F₆) at a sufficiently high rate andmoreover, a separate secondary treatment of compounds such as SiF₄contained in the exhaust gas after the decomposition is necessary.According to the method (3), decomposition may be performed at arelatively low temperature as compared with the methods (1) and (2),however, the following problems still remain. For decomposing PFC in anamount of 100%, the supply gas must be diluted with air or the like toreduce the PFC concentration in the gas. Furthermore, in order to bringout the catalytic action of alumina, it is necessary to allow a largeamount of steam to be present together and thereby hydrolyze, forexample, fluoride or the like accumulated on the alumina surface.Therefore, an anticorrosive material against HF generated by thehigh-temperature decomposition of fluoride on the alumina surface, and asecondary treatment of HF are necessary.

As such, a method for effectively decomposing fluorine compounds usingan industrially advantageous process is heretofore not known and moreimprovements are demanded.

SUMMARY OF THE INVENTION

An object of the present invention is to solve the above-describedproblems and provide a reactive agent which can thermally decomposefluorine compounds at a relatively low temperature without adding waterand which can fix the decomposition products (e.g., F, SO_(x)) of thedecomposed fluorine compound to the reactive agent.

Another object of the present invention is to provide a process forefficiently decomposing particularly PFC which is difficult todecompose.

As a result of extensive investigations to solve the above-describedproblems, the present inventors have found that these objects can beattained by a reactive agent for decomposing fluorine compounds,comprising alumina and an alkaline earth metal compound. Furthermore,the present inventors have found that in a process for decomposingfluorine compounds, comprising contacting a fluorine compound with theabove-described reactive agent at a temperature of 200° C. or more, thefluorine compound can be thermally decomposed, the generated chlorineatoms, fluorine atoms and/or sulfur atoms can be fixed as a chloride, afluoride and/or a sulfate of an alkaline earth metal in the reactiveagent, and if desired, by adding a metal oxide to the reactive agent toincorporate oxygen into the fluorine compound, the carbon monoxidegenerated can be simultaneously oxidized and thereby detoxified. Thepresent invention has been accomplished based on these findings. Thepresent invention relates to a reactive agent and a process fordecomposing fluorine compounds, described in (1) to (28) below:

(1) A reactive agent for decomposing fluorine compounds, comprisingalumina and an alkaline earth metal compound;

(2) the reactive agent for decomposing fluorine compounds as describedin (1) above, wherein the alumina has a specific surface area of 50 m²/gor more;

(3) the reactive agent for decomposing fluorine compounds as describedin (1) or (2) above, wherein the alumina is pseudo boehmite alumina;

(4) the reactive agent for decomposing fluorine compounds as describedin (1) or (2) above, wherein the alumina is obtained by baking pseudoboehmite alumina at a baking temperature of from 400 to 1,000° C.;

(5) the reactive agent for decomposing fluorine compounds as describedin any one of (1) to (4) above, wherein the alkaline earth metalcompound is a carbonate of magnesium, calcium, strontium or barium;

(6) the reactive agent for decomposing fluorine compounds as describedin any one of (1) to (5) above, wherein the alumina and the alkalineearth metal compound present in the reactive agent each is in the formof a powder having a particle size of 100 μm or less;

(7) the reactive agent for decomposing fluorine compounds as describedin any one of (1) to (6) above, wherein the alumina and the alkalineearth metal compound are present in the reactive agent at a mass ratioof from 1:9 to 1:1;

(8) the reactive agent for decomposing fluorine compounds as describedin any one of (1) to (7) above, which contains at least one oxide of ametal selected from the group consisting of copper, tin, nickel, cobalt,chromium, molybdenum, tungsten and vanadium;

(9) the reactive agent for decomposing fluorine compounds as describedin (8) above, wherein the content of the metal oxide is, in terms of aratio to the total mass of the alumina and alkaline earth metalcompound, from 1:99 to 5:95;

(10) the reactive agent for decomposing fluorine compounds as describedin any one of (1) to (9), which has an alkali metal content of 0.1 mass% or less;

(11) the reactive agent for decomposing fluorine compounds as describedin any one of (1) to (10) above, which is a granular product obtained bybaking at a temperature of from 400 to 700° C.;

(12) the reactive agent for decomposing fluorine compounds as describedin (11) above, which is a granular product having a particle size offrom 0.5 to 10 mm;

(13) the reactive agent for decomposing fluorine compounds as describedin any one of (1) to (12) above, which has a water content of 1 mass %or less.

(14) the reactive agent for decomposing fluorine compounds as describedin any one of (1) to (13) above, wherein the fluorine compound is atleast one fluorine compound selected from the group consisting ofperfluorocarbon, hydrofluorocarbon, chlorofluorocarbon,hydrochlorofluorocarbon, perfluoroether, hydrofluoroether, fluoroolefin,sulfur fluoride, SiF₄ and COF₂;

(15) the reactive agent for decomposing fluorine compounds as describedin (14) above, wherein the fluorine compound contains hydrogen chlorideand/or hydrogen fluoride;

(16) a process for decomposing fluorine compounds, comprising contactinga reactive agent described in any one of (1) to (15) above with afluorine compound at a temperature of 200° C. or more;

(17) the process for decomposing fluorine compounds as described in (16)above, wherein the fluorine compound concentration in a gas to betreated by contacting it with a reactive agent described in any one of(1) to (15) above is from 0.01 to 10 vol %;

(18) a process for decomposing fluorine compounds, comprising contactinga reactive agent described in any one of (1) to (15) above with afluorine compound at a temperature of 500° C. or more in the presence ofoxygen gas, thereby controlling the generation of carbon monoxide;

(19) the process for decomposing fluorine compounds as described in (18)above, wherein the oxygen gas concentration in a gas to be treated is 20vol % or less;

(20) the process for decomposing fluorine compounds as described in anyone of (16) to (19) above, wherein chlorine atom, fluorine atom and/orsulfur atom produced on contacting a reactive agent described in any oneof (1) to (15) above with a fluorine compound are fixed as an alkalineearth metal chloride, an alkaline earth metal fluoride and/or analkaline earth metal sulfate, respectively;

(21) a process for manufacturing a semiconductor device, comprising anetching or cleaning step of using as an etching gas or cleaning gas atleast one fluorine compound selected from the group consisting ofperfluorocarbon, hydrofluorocarbon, chlorofluoro carbon,hydrochlorofluorocarbon, perfluoroether, hydrofluoroether, fluoroolefinand sulfur fluoride, and a decomposition step of decomposing thefluorine compound-containing gas discharged from the etching or cleaningstep using a reactive agent described in any one of (1) to (15) above;

(22) the process for manufacturing a semiconductor device as describedin (21) above, wherein the gas discharged from the etching or cleaningstep is a gas containing at least one fluorine compound selected fromthe group consisting of perfluorocarbon, hydrofluorocarbon,chlorofluorocarbon, hydrochlorofluorocarbon, perfluoroether,hydrofluoroether, fluoroolefin, sulfur fluoride, SiF₄ and COF₂;

(23) the process for manufacturing a semiconductor device as describedin (22) above, wherein the fluorine compound-containing gas containshydrogen chloride and/or hydrogen fluoride;

(24) the process for manufacturing a semiconductor device as describedin any one of (21) to (23) above, wherein in the decomposition step, thefluorine compound in a gas to be treated is decomposed at a temperatureof 200° C. or more;

(25) the process for manufacturing a semiconductor device as describedin any one of (21) to (24) above, wherein in the decomposition step, thefluorine compound concentration in a gas to be treated is from 0.01 to10 vol %;

(26) a process for manufacturing a semiconductor device comprising thedecomposition step is performed at a temperature of 500° C. or more inthe presence of oxygen gas, thereby controlling the generation of carbonmonoxide;

(27) the process for manufacturing a semiconductor device as describedin (26) above, wherein in the decomposition step, the oxygen gasconcentration in a gas to be treated is 20 vol % or less;

(28) the process for manufacturing a semiconductor device as describedin any one of (21) to (27) above, wherein chlorine atom, fluorine atomand/or sulfur atom produced in the decomposition step of decomposing thegas discharged from the etching or cleaning step using a reactive agentdescribed in any one of (1) to (15) above are fixed as an alkaline earthmetal chloride, an alkaline earth metal fluoride and/or an alkalineearth metal sulfate, respectively.

In summary, the present invention provides “a reactive agent fordecomposing fluorine compounds, comprising alumina and an alkaline earthmetal compound, which can decompose and detoxify fluorine compoundshaving a high ozone layer destruction coefficient or a high globalwarming potential coefficient”, “a process for decomposing fluorinecompounds, comprising contacting a fluorine compound with theabove-described reactive agent at a temperature of 200° C. or more”, “aprocess for decomposing fluorine compounds, comprising incorporatingoxygen into a fluorine compound and contacting the fluorine compoundwith the above-described reactive agent at a temperature of 500° C. ormore, thereby controlling the generation of carbon monoxide”, and “aprocess for manufacturing a semiconductor device, comprising an etchingor cleaning step and a decomposition step of decomposing a gascontaining fluorine compounds discharged from the etching or cleaningstep using the above-described reacting agent”.

According to the above-described conventional techniques, namely, (1) acombustion decomposition method, (2) a thermal decomposition methodusing a reactive agent and (3) a decomposition method using an aluminacatalyst, the decomposition product of fluorine compounds is a substancestill having harmful effect on the environment. Therefore, a treatmentfor detoxifying the decomposition product must be separately employed inthe later stage of the decomposition step. This makes it difficult todownsize the apparatus. In particular, the gases discharged from themanufacturing process of semiconductor devices, for example, PFC exhaustgas used for etching or cleaning contains fluorine compounds such as HF,SiF₄ and COF₂ in addition to PFC. Accordingly, in the case of thecatalytic decomposition method, a treatment for the detoxification ofSiF₄ and the like is necessary also in the early stage and a complicatedand cumbersome apparatus is required. Furthermore, for the decompositionof PFC which is particularly difficult to decompose, a high temperatureis necessary but this gives rise to a problem that the material of whichthe reactor is constructed deteriorates.

On the other hand, according to the present invention, a fluorinecompound used for the purpose of electrical insulation, as a refrigerantor in the process of manufacturing semiconductor devices can beefficiently decomposed at a low temperature. In the present invention,the fluorine compound is decomposed simultaneously with SiF₄ and thelike generated when the fluorine compound is used, for example, inetching. Furthermore, a reaction for fixing and thereby detoxifying, forexample, fluorine generated by the decomposition as an alkaline earthmetal fluoride (for example, as CaF₂) proceeds at the same time.Therefore, the problems in this concern can also be solved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a systematic diagram of equipment layout showing one exampleof the apparatus used in the practice of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is described in detail below.

The fluorine compounds which can be decomposed by the reactive agent ofthe present invention are described. Examples of CFC include compoundssuch as CClF₃, CC₁ ₂F₂, CCl₃F, C₂Cl₃F₃, C₂Cl₂F₄ and C₂ ClF₅. Examples ofHCFC include compounds such as CHClF₂ and C₂HCl₂F₃. Examples of PFCinclude CF₄, C₂F₆, C₃F₈ and C₄F₈ (octafluorocyclobutane). Examples ofHFC include compounds such as CH₃F, CH₂F₂, CHF₃ and C₂H₂F₄. Examples ofPFE include compounds such as CF₃OCF₃ and CF₃OCF₂CF₃. Examples of HFEinclude compounds such as CHF₂OCHF₂, CHF₂OCH₂CF₃ and CH₃OCF₂CF₃.Examples of sulfur fluoride include compounds such as SF₆ and S₂F₁₀. Thereactive agent of the present invention may also be applied to compoundsother than these fluorine compounds. For example, compounds such asCF₃OCF═CF₂ which is an unsaturated compound, and C₅F₈(octafluorocyclopentene), or compounds present in the exhaust gasdischarged after PFC is used in the etching step, such as HF, SiF₄ andCOF₂, may be similarly decomposed and detoxified.

These fluorine compounds may be diluted with an inert gas such ashelium, argon or nitrogen, or with air, or may be a mixed gas containing0.01 vol % or more of a vapor of the fluorine compound (which is liquidat an ordinary temperature) when accompanied by an inert gas or air. Thefluorine compound may be a single compound or a mixture of two or morecompounds.

The reactive agent for decomposing fluorine compounds of the presentinvention is described below.

The reactive agent for decomposing fluorine compounds of the presentinvention is characterized in that it contains an alumina and analkaline earth metal compound. The alumina in the reactive agent is arepresentative acidic substance (solid acid) and known to decomposefluorine compounds by itself. For example, Shokubai (Catalyst), Vol. 34,No. 7, pp. 464-469 (1992) describes the use of alumina as a catalyst fordecomposing CFC. Briefly, when CFC is decomposed using alumina (Al₂O₃),the alumina surface is fluorinated by fluorine generated at thedecomposition. Thus, the alumina is poisoned by AlF₃ and thereby losesits catalytic activity within a short time. However, metal halidecompounds in general are readily hydrolyzed at a high temperature and bymaking use of this property, when hydrolysis of AlF₃ is performed in thepresence of steam together (2AlF₃+3H₂O→Al₂O₃+6HF), the aluminaregenerated can be catalytically used. This reaction in the presence ofwater, however, has a problem in that hydrogen fluoride is generated bythe decomposition of AlF₃ and corrodes the apparatus. To solve thisproblem, the present inventors have made various studies on thedecomposing agent capable of continuously decomposing fluorinecompounds, in particular, PFC which is difficult to decompose, at a lowtemperature in the absence of water. As a result, it has been found thatwhen a reactive agent comprising alumina and an alkaline earth metalcompound is used, fluorine compounds can be decomposed at a reactiontemperature of 200° C. or more and hydrogen fluoride generated can befixed as an alkaline earth metal fluoride, thereby attainingdetoxification without causing corrosion of the apparatus.

Depending on the kind of the fluorine compound, the reactive agent fordecomposing fluorine compounds of the present invention, comprisingalumina and an alkaline earth metal compound, may generate carbonmonoxide as shown below:

(1) CF₄+2CaCO₃/Al₂O₃→2CaF₂+3CO₂

(2) C₂F₆+3CaCO₃/Al₂O₃→3CaF₂+4CO₂+CO

The carbon monoxide can be oxidized under a sufficiently large oxygenpartial pressure. However, in the case where the oxygen partial pressureis limited, it has been found, by adding at least one oxide of a metalselected from the group consisting of copper, tin, nickel, cobalt,chromium, molybdenum, tungsten and vanadium, to the reactive agent, thecarbon monoxide can be oxidized into carbon dioxide even under a lowoxygen partial pressure. This metal oxide is considered to serve also asa co-catalyst of breaking the carbon-carbon bond of the fluorinecompound.

The alumina used in the present invention is not particularly limited,however, it is important to select an alumina having a sufficientlylarge number of active sites which result in the decomposition offluorine compound and a sufficiently large specific surface area,namely, pores (size and volume of pore) which result in the adsorptionof fluorine compound. Accordingly, the alumina preferably has a specificsurface area of 50 m²/g or more, more preferably from 100 to 300 m²/g.Also, it is important to select an appropriate starting material with areduced level of impurities. Examples of the alumina raw material whichcan be used in the present invention include an active alumina and apseudo boehmite alumina. Among these, pseudo boehmite alumina ispreferred. The pseudo boehmite alumina may be mixed as it is with analkaline earth metal compound and used. In the case of baking the pseudoboehmite alumina, the baking may be sufficient if it is performed in aninert gas such as nitrogen or in air at from 400 to 1,000° C.,preferably from 500 to 800° C., more preferably from 500 to 600° C., fora few hours.

The content of alkali metals present as impurities in the alumina issuitably 0.1 mass % or less, preferably 0.01 mass % or less, morepreferably 0.001 mass % or less. Furthermore, the particle size of thealumina is 100 μm or less, preferably 30 μm or less, more preferably 5μm or less, and alumina in the powder form is used.

The alkaline earth metal compound as another component of the reactiveagent is described below.

The alkaline earth metal compound is preferably a carbonate ofmagnesium, calcium, strontium or barium, more preferably a carbonate ofcalcium. In the case where, for example, calcium carbonate is used inthe reactive agent, the calcium carbonate present together with aluminafixes fluorine generated by the decomposition of fluorine compound asCaF₂ and thereby prevents the fluorination of alumina, so that thealumina maintains the function (activity) of decomposing fluorinecompounds.

In the alkaline earth metal compound, similarly to the alumina, thecontent of alkali metals present as impurities is suitably 0.1 mass % orless, preferably 0.01 mass % or less, more preferably 0.001 mass % orless. The particle size of the alkaline earth metal compound ispreferably 100 μm or less, preferably 30 μm or less, more preferably 5μm or less, and an alkaline earth metal compound in the powder form isused. The alkaline earth metal compound and the alumina used both have aparticle size of 100 μm or less because since respective raw materialsare fine powder and easily dispersed with each other, the specificsurface area of each raw material increases to allow the alumina and thealkaline earth metal compound to come close without limit and contacteach other, whereby the opportunity of fluorine generated by thedecomposition of the fluorine compound on the alumina surface reactingwith the alkaline earth metal compound increases. Accordingly, thespecific surface area of the alkaline earth metal compound is suitably 5m²/g or more. Specific examples of the calcium carbonate raw materialwhich can be particularly preferably used include heavy calciumcarbonate (obtained by pulverizing limestone), light calcium carbonate(also called precipitated calcium carbonate, obtained by blowing carbondioxide into milk of lime), and quick lime and slaked lime which areneutralized with carbonic acid. Among these, light calcium carbonatewith reduced level of impurities such as alkali metal is preferred, andhigh-purity calcium carbonate is more preferred.

The mechanism how the reactive agent of the present invention decomposesfluorine compounds at a low temperature is not clearly known. However,since almost no effect is provided by a metal oxide such as iron oxideand manganese oxide, a peculiar composite effect is considered to occurwhen an alumina and an alkaline earth metal compound, particularly analumina and a carbonate of an alkaline earth metal, are presenttogether.

The oxide of copper, tin, nickel, cobalt, chromium, molybdenum, tungstenor vanadium, as still another component of the reactive agent of thepresent invention, is described below.

At least one metal oxide selected from the group consisting of copperoxide, tin oxide, nickel oxide, cobalt oxide, chromium oxide, molybdenumoxide, tungsten oxide and vanadium oxide can be added to the reactiveagent. Among these metal oxides, copper oxide, tin oxide and vanadiumoxide are preferred, and copper oxide and tin oxide are more preferred.Although the metal oxide is considered to serve also as a co-catalystfor decomposing fluorine compounds, when copper oxide or tin oxide, forexample, is used in the reactive agent and allowed to be presenttogether with alumina and an alkaline earth metal compound, depending onthe kind of the fluorine compound, the carbon monoxide generated by thedecomposition can be oxidized into carbon dioxide under a low oxygenpartial pressure.

In the metal oxide, similarly to the above-described raw materials ofthe reactive agent, the content of alkali metals present as impuritiesis 0.1 mass % or less, preferably 0.01 mass % or less, more preferably0.001 mass % or less. The particle size of the metal oxide is suitably100 μm or less, preferably 30 μm or less, more preferably 5 μm or less,and a metal oxide in a powder form is used.

The manufacturing process of the reactive agent of the present inventionis described below.

The process for decomposing fluorine compounds according to the presentinvention comprises the use of a reactive agent comprising alumina andan alkaline earth metal compound. The content ratio of the alumina andthe alkaline earth metal compound present in the reactive agent issuitably, in terms of the mass ratio, from 1:9 to 1:1, preferably from1:4 to 2:3. The alumina in the reactive agent efficiently decomposesfluorine compounds when it is present together with an alkaline earthmetal compound and the content of the alumina may vary as thedecomposition reaction proceeds. However, at least in the initial stageof the decomposition reaction, the alumina is preferably present in anamount of 0.1 or more in terms of a mass ratio to the entire reactiveagent of which mass is taken as 1. If the mass ratio is less than 0.1,the decomposition of the fluorine compounds may not proceedsatisfactorily, whereas if the alumina is present in an amount in excessof 0.5 in terms of the mass ratio, the amount of the alkaline earthmetal compound decreases in proportion and the effective utilizationfactor of the reactive agent decreases.

The content ratio of the metal oxide is preferably, in terms of theratio to the total mass of the alumina and the alkaline earth metalcompound, from 1:99 to 5:95. If this mass ratio is excessively small,the effect cannot be obtained, whereas if it is excessively large, thetotal amount of the alumina and the alkaline earth metal compoundrelatively decreases and the effect of the metal oxide is saturated,therefore, the decomposition of fluorine compounds cannot proceedefficiently.

The reactive agent for decomposing fluorine compounds of the presentinvention can be prepared by mixing the alumina and the alkaline earthmetal compound at the above-described mass ratio and if desired, byadding a metal oxide, and may be used as it is. Here, the water contentin respective raw materials is preferably reduced as low as possible.The water content in the reactive agent is preferably 1 mass % or less.

The reactive agent can also be prepared by granulating those rawmaterials and may be used as a granule. In forming the reactive agent bygranulation, water or depending on the particle size of the rawmaterials, water and a binder may be added. The binder is notparticularly limited as long as it does not affect the raw materialsblended, and may be added in an amount of from 0.03 to 0.05 in terms ofthe mass ratio to the total mass of the raw materials blended which istaken as 1.0. The binder is preferably fine powder alumina. By addingfine powder alumina, respective raw materials are more improved in thedispersibility, and difficulty in the granulation of an alkaline earthmetal compound can be overcome. In the alumina added as the binder, theparticle size is suitably 0.1 μm or less, and the content of alkalimetals contained as impurities is suitably 0.1 mass % or less,preferably 0.01 mass % or less. This fine powder alumina is advantageousin that the effect can be obtained even with a small amount and therelative contents of effective components per unit volume of thereactive agent scarcely decrease. However, as long as the binder doesnot affect the capability of the reactive agent obtained, the kind andthe amount of the binder are not limited.

As described above, each of the raw materials blended in the reactiveagent, including the fine powder alumina added as the binder, preferablyhas an alkali metal content of 0.1 mass % or less. If the alkali metalcontent in the reactive agent exceeds 0.1 mass %, the active sites onthe alumina surface decrease and thereby the decomposition ratioparticularly of PFC such as CF₄ and C₂F₆ is reduced.

In manufacturing the granular reactive agent for use in the presentinvention, respective raw materials are blended and then kneaded whileadding an appropriate amount of water, and the kneaded product isgranulated to provide a granular article. As the kneader necessary forthe preparation of this granular article, those capable of performingmixing and granulation at the same time are convenient, however, thosewhere the mixing and the granulation are separately performed may alsobe used. For example, when a Henschel mixer or a vertical mixer is used,the mixing and the granulation can be performed at the same time.However, it is also possible to mix the raw materials in a Henschelmixer or a V-type mixer and granulate the mixture in a pan-typepelletizer or a drum pelletizer.

The granular article is then dried at from 100 to 200° C. in an inertgas such as nitrogen or in air so as to evaporate water. The reasons whythe reactive agent is used as a granular article are to have highdecomposing activity of the reactive agent and to increase hardness andthereby to prevent crushing or flouring during filling into a reactor orhandling. For this purpose, it is preferable to further bake thegranular article. More specifically, the granulated and dried article isbaked at from 400 to 700° C., preferably from 500 to 700° C. in an inertgas such as nitrogen or in air. The reasons for baking at 400° C. ormore is that the water added during the granulation can be furtherevaporated to increase the decomposing activity and that the hardnesscan be further increased. If the baking temperature exceeds 700° C., thedecomposing ratio (activity) of the reactive agent decreases though itis not clearly known whether this is ascribable to the decomposition ofthe alkaline earth metal compound (for example, CaCO₃→CaO+CO₂). In otherwords, it is important to almost completely dehydrate the bound water ofalumina at 700° C. or less where the activity of reactive agent does notdecrease. The water content in the baked reactive agent is preferablysuch that the amount of water content released on heating at 550° C. inan inert gas or air is 1 mass % or less. The baking may be performed incontinuous equipment such as rotary kiln but may also be performed in astationary furnace.

As described above, the reactive agent for decomposing fluorinecompounds of the present invention comprises alumina and an alkalineearth metal compound as essential components. In the case where carbonmonoxide is generated, the reactive agent can also contain at least oneoxide of a metal selected from the group consisting of copper, tin,nickel, cobalt, chromium, molybdenum, tungsten and vanadium, so as tooxidize the carbon monoxide into carbon dioxide even under a low oxygenpartial pressure. The reactive agent is preferably in the granular formfor increasing opportunities of contact with a fluorine compound to bedecomposed. If the particle size is excessively large, the surface areaparticipating in the adsorption and diffusion of the fluorine compoundgas is relatively reduced and the diffusion rate becomes lower. On theother hand, if the particle size is excessively small, the surface areaparticipating in the adsorption and diffusion of the fluorine compoundgas is relatively increased and the diffusion rate becomes higher.However, the amount of gas to be treated increases to give a largedifferential pressure and this prevents the reduction in the size ofreactor or the like. Accordingly, the particle size of the reactiveagent is suitably from 0.5 to 10 mm, preferably from 1 to 5 mm.

The process for decomposing fluorine compounds according to the presentinvention is described below.

When the reactive agent produced by the method described above iscontacted with a fluorine compound at an appropriate temperature, thefluorine compound is decomposed and the chlorine atom and/or fluorineatom generated by the decomposition is fixed to the reactive agent as achloride and/or a fluoride of an alkaline earth metal. In the case wherethe gas to be treated contains a sulfur fluoride such as SF₆, the sulfuratom generated by the decomposition is fixed to the reactive agent as asulfate of an alkaline earth metal, thus, the generation of sulfuroxides can be controlled.

In other words, when the reactive agent for decomposition of the presentinvention is used, fluorine compounds can be efficiently decomposedwithout releasing harmful decomposition product gases, for example,compounds such as HF, SiF₄, COF₂ and SO_(x). However, in order toprevent such decomposition products from remaining in the decomposedgas, the reaction conditions must also be appropriately controlled, suchas the reaction temperature, the concentrations of fluorine compounds inthe gas to be treated, the presence or absence of oxygen in the gas tobe treated, the form of the reactive agent, and the rate of supplyingthe gas to be treated. Among these, the reaction (decompositioninitiating) temperature is a very important condition.

The reaction temperature varies depending on the kind of the fluorinecompound present in the gas to be treated.

For example, PFC is classified into compounds which are difficult todecompose out of fluorine compounds. In particular, CF₄, C₂F₆ and thelike are most difficult to decompose, and for decomposing these only bymere thermal decomposition, a high temperature of from 1,200 to 1,400°C. is necessary. However, according to the process of the presentinvention, these can be decomposed at 550° C. or more. Furthermore,CHClF₂ which is an HCFC can be decomposed at a temperature of 200° C. ormore by the process of the present invention. As such, the decompositiontemperature varies by a fairly large range depending on the kind offluorine compound. Therefore, it is important to set the reactor at anoptimal temperature according to the kind of compound to be decomposed.

Since the reaction temperature thus varies depending on the kind orstructure of compound, when the gas to be treated contains multiplekinds of PFC or HFC as in the gas discharged from the etching orcleaning step in the process of manufacturing semiconductor devices, thereaction temperature is set at 550° C. or more to detoxify all of thesefluorine compounds. In the case where, for example, a carbonate is usedas the alkaline earth metal compound, carbons originated from thefluorine compound are oxidized by oxygen released upon decomposition ofthe carbonate and mostly released as CO₂. Depending on the kind offluorine compound, CO may be generated. However, by allowing oxygen tobe present in the gas to be treated, CO is easily oxidized into CO₂ withthe same reactive agent and can be completely detoxified.

In other words, the process for decomposing fluorine compounds accordingto the present invention can be performed by passing a gas containingfluorine compounds through a reactor filled with the reactive agent,while maintaining the decomposition temperature according to thedecomposability of the fluorine compound. Even if the reactionatmosphere is a non-oxidative atmosphere, the object may be fullyattained. However, for reducing CO to an acceptable concentration orless, the treatment is performed in an oxidative atmosphere, forexample, in an atmosphere where 20 vol % or less of oxygen gas ispresent in the gas to be treated. In this atmosphere, CO can also besimultaneously treated. The oxygen gas concentration is 20 vol % or lessbecause air is preferably used as the diluting gas. Even if the oxygengas concentration is higher than this range, the effect is saturated andthe decomposing activity does not increase any more.

The fluorine compound concentration in the gas to be treated is notparticularly limited, however, an excessively low concentration isdisadvantageous in view of profitability. On the other hand, if theconcentration is excessively high, the reaction temperature increasesdue to the heat generated by the decomposition though this may varydepending on the kind of fluorine compound, and sometimes thetemperature within the reactor can be hardly controlled. Therefore, thegas to be treated is preferably diluted with an inert gas or an oxygengas-containing gas (including air) such that the fluorine compoundconcentration becomes from 0.01 to 10 vol %, preferably from 0.01 to 5vol %, more preferably from 0.01 to 3 vol %. The fluorine compoundconcentration in the gas is not particularly limited to thisconcentration when the heat generated by the decomposition can beremoved affirmatively and the reaction temperature can be controlled.

In this way, preferred reaction conditions are established according torespective cases by taking account of the kind and concentration of thefluorine compound in the gas subjected to the decomposition treatment,the oxygen gas concentration in the gas to be treated, SV (spacevelocity), LV (linear velocity) and the mixed state with other gases.

The decomposition treatment may be performed using a decompositionapparatus comprising a reactor filled with the above-described reactiveagent, an inlet for the gas to be treated, which is provided tocommunicate with the inside of the reactor, a gas outlet for dischargingthe gas out of the reactor after the reaction, a furnace for housing thereactor and a heat source for elevating the furnace atmosphere to apredetermined temperature, by connecting the inlet for gas to be treatedand a fluorine compound gas source through a pipeline.

FIG. 1 is a view showing one example of the apparatus for practicing thepresent invention. While previously allowing a constant amount of acarrier gas to flow through a nitrogen gas supply line 2 or an air oroxygen gas supply line 3, a preheating zone 9 for heating the gas to betreated in a reactor 8 and a reactive agent 12 filled downstream areheated to a predetermined temperature by an electric heater 11 using atemperature sensor 7 provided in the reactor 8 and a temperaturecontrolling unit 10, and then controlled at a constant temperature.

After the control to a predetermined temperature, gases to be treatedare introduced into a mixing chamber and a header 4 through respectivevalves from a fluorine compound gas supply line 1 and a nitrogen gassupply line 2 or an air or oxygen supply line 3. The mixed gas to betreated is introduced into the reactor 8 through a gas inlet tube 6. Thegas to be treated, which is introduced into the reactor 8 and heated inthe preheating zone 9, is contacted with the reactive agent heated to apredetermined temperature and thereby decomposed. After thedecomposition, the treated gas (exhaust gas) is cooled to apredetermined temperature by a cooler 14 (either water cooling or aircooling is possible) and discharged from a discharge tube 16. Forsampling a gas, sampling ports for the gas to be treated 5 and for thetreated gas 15 may be provided in the vicinity of inlet and outlet portsof the reactor 8 and thereby the components of each gas may be analyzed.

As such, the fluorine compounds in the gas to be treated can be almostcompletely (in a decomposition ratio of nearly 100%) decomposed. Thefluorine component in the decomposed fluorine compound is fixed to thereactive agent as a stable alkaline earth metal fluoride such as CaF₂and the carbon component is mostly discharged as CO₂ together with thediluting gas such as nitrogen gas. Accordingly, the treated gas is aharmless gas substantially free of residual harmful materials such asfluorine component or carbon monoxide.

The decomposition reaction terminates when the reactive agent present isused up. This end of the decomposition reaction is known by the timewhen the fluorine compound is first detected. The fluorine compound maybe decomposed in a batch system where when the fluorine compound isdetected and the reactive agent loses the decomposing activity, theapparatus stops the operation and after newly filling the reactiveagent, the decomposition reaction re-starts, or by sequentiallyexchanging the reactor with spare reactors previously filled with thereactive agent in the same apparatus.

In order to continuously use the batch system, a multiple tower switchsystem may also be adopted, where a plurality of reactors of the sametype are juxtaposed, the reactive agent of one reactor is exchangedwhile another reactor is operating, or the reactor is exchanged with aseparate reactor previously filled with a reactive agent, and when onereactor is stopped, the gas passage is switched to another reactor.Furthermore, when the apparatus used is designed to have a function ofcontinuously or intermittently supplying the reactive agent into thereactor and continuously or intermittently discharging the used reactiveagent from the reactor, the operation can be continuously performed fora long period of time in the same apparatus.

As described above, according to the present invention, the fluorinecompound can be decomposed with good efficiency and the gas dischargedis substantially free of residual harmful materials such as fluorinecomponent or carbon monoxide. The fluorine compound described here is acompound which can be used as an etching gas in the etching step or as acleaning gas in the cleaning step during the process of manufacturingsemiconductor devices, and this is at least one fluorine compoundselected from the group consisting of perfluorocarbon,hydrofluorocarbon, chlorofluoro carbon, hydrochlorofluorocarbon,perfluoroether, hydrofluoroether, fluoroolefin and sulfur fluoride. Thepresent invention is a process for manufacturing a semiconductor device,comprising an etching or cleaning step of using the above-describedfluorine compound as an etching or cleaning gas and a decomposition stepof decomposing a fluorine compound-containing gas discharged fromthe-etching or cleaning step using the reactive agent comprising aluminaand an alkaline earth metal compound, where the fluorinecompound-containing gas can be decomposed and detoxified with goodefficiency.

In the process for manufacturing a semiconductor device such as LSI andTFT, a thin or thick film is formed using a CVD method, a sputteringmethod or a vacuum evaporation method, and then a circuit pattern isformed by etching. In the apparatus for forming the thin or thick film,cleaning is performed so as to remove unnecessary deposits accumulatedon inner walls of the apparatus or jigs. The accumulated unnecessarydeposits cause generation of particles, therefore, must be removed onoccasion for producing a good film.

The etching method using, for example, the above-described fluorinecompound can be performed under various dry etching conditions such asplasma etching and microwave etching. The gas discharged from theetching step may contain, for example, compounds such as SiF₄ and COF₂or gases such as hydrogen chloride and hydrogen fluoride, in addition tothose fluorine compounds. However, as described above, by using thereactive agent of the present invention, these compounds and gases canbe simultaneously decomposed and the chlorine or fluorine atom can befixed as a chloride or a fluoride of an alkaline earth metal or thecarbon atom can be decomposed into carbon dioxide and thus detoxified.

Depending on the kind of the fluorine compound, CO may be generated.However, by allowing an oxygen gas to be present during thedecomposition step with the gas to be treated, CO can be easily oxidizedinto CO₂ and thus can be completely detoxified.

Furthermore, the process of the present invention can be used in theprocess for manufacturing semiconductor devices described inJP-A-10-12605 and JP-A-2000-58840.

The present invention is described in greater detail below by referringto Examples, however, the present invention should not be construed asbeing limited thereto. Unless otherwise indicated herein, all percents,parts ratios and the like are by weight.

PREPARATION EXAMPLE OF REACTIVE AGENTS

Various raw materials of reactive agents used in tests are shown inTable 1.

TABLE 1 Specific Name of Raw Particle Surface Materials of Size AreaImpurities (mass %) Reactive Agent (μm) (m²/g) Na K Fe Si CaCO₃-a(high-purity 40 — 0.0012 0.0005 <0.0001 <0.0001 calcium carbonate)CaCO₃-b (light 50 — 0.0056 0.0008 0.0010 0.001 calcium carbonate)CaCO₃-c (heavy 45 — 0.0104 0.0027 0.0050 0.09 calcium carbonate) SrCO₃(strontium — — 0.0107 0.001 0.005 — carbonate) Al₂O₃-a [AlO(OH)] 60 2410.0027 <0.001 Fe₂O₃ SiO₂ (pseudo boehmite 0.0034 0.0066 alumina) Al₂O₃-b[Al₂O₃] — 173 — — — — (Al₂O₃-a baked at 550° C. for 3 hours) Al₂O₃-c(active 10 255 0.067 <0.001 Fe₂O₃ SiO₂ alumina) 0.03 0.01 Al₂O₃-d(active 5 201 0.28 <0.001 Fe₂O₃ SiO₂ alumina) 0.01 0.01 CuO (cupricoxide) 4-10 — <0.01 <0.01 <0.01 <0.05 SnO₂ (stannic oxide) 4-10 — <0.01<0.01 <0.01 <0.05 V₂O₅ (vanadium 4-10 — <0.01 <0.01 <0.01 <0.05pentoxide) Cr₂O₃ (chromium 10 — <0.01 <0.01 <0.01 — oxide) Binder I(ultrafine <0.1 — <0.001 <0.001 <0.001 <0.001 powder alumina) Binder II(clay) 50 — Na₂O K₂O Fe₂O₃ SiO₂ 0.06 0.07 2.13 57.73

In Table 1, with respect to the same raw materials of the reactiveagent, an alphabetic designation (for example, CaCO₃-a) or an Arabicfigure designation is affixed to the chemical formula so as todifferentiate the materials by grades. This differentiation also appliesto the materials in Tables 2 to 6 showing Examples and ComparativeExamples.

Using the materials shown in Table 1 as the raw materials, granulararticles having a particle size of from 0.85 to 2.8 mm were produced.More specifically, the materials shown, for example, in Test Condition 1of Table 2 and a binder were blended, mixed in a Henschel mixer and,after adding water thereto, granulated. The resulting granulate wasdried at 110° C. for 3 hours and then sieved. Each of the granulararticles produced was dehydration baked by a heat treatment at a bakingtemperature of 550° C. or 700° C. (electric furnace) shown in TestCondition 2 of Table 2 for 3 hours in an air atmosphere to prepare areactive agent.

REACTION EXAMPLE

The process of the present invention was performed using an apparatushaving the same arrangement as the apparatus shown in FIG. 1. Namely,along the center of axis of a cyclic furnace (electric capacity: 1.4 KW,length: 400 mm) with heating elements (kanthal alloy) capable ofgenerating heat on passing of electricity, a reaction tube comprisingInconel 600 (or SUS310S) and having an internal diameter of 16 mm and alength of 500 mm was pierced and 35 ml of a reactive agent fordecomposing fluorine compounds was filled in the furnace center of thereaction tube.

Fluorine compounds to be decomposed were used and as shown in FIG. 1,after adding or not adding oxygen gas thereto, the fluorine compoundswere introduced into the above-described reaction tube using nitrogengas as a carrier. At this time, the conditions were as follows.

Flow rate of gas to be treated 0.201/min Concentration of fluorinecompound in gas to be 0.5 to 3 vol % treated: Space velocity of gas tobe treated: 343 hr⁻¹ Linear velocity of gas to be treated: 1.0 m/minConcentration of oxygen gas in the gas to be treated: 20 vol % or less

In some tests, HF, SiF₄ or CO gas was allowed to be present together inthe gas to be treated, or reaction tubes were connected.

In each Example, the gas to be treated was introduced after startingcharging of the heating element while controlling the quantity ofelectricity in the cyclic furnace so that the temperature measured by athermocouple inserted into the center part of the reactive agent (thesite reaching a highest temperature in the bulk of the reactive agent)could be maintained at a predetermined temperature. In the respectiveTables, the reaction temperature indicates this temperature maintainedduring the reaction.

The gas to be treated and the treated gas were sampled from respectivesampling ports shown in FIG. 1 and the composition analyzed. O₂, N₂, CO,CO₂ and fluorine compounds were analyzed using a gas analyzer, and F ionwas sampled in a fluorine absorbing bottle containing a sodium hydroxidesolution and analyzed.

The reactive agent compositions (combinations of materials) and thebinders shown in Test Condition 1 of Tables 2 to 6 correspond torespective raw material names of the reactive agent shown in Table 1.For example, high-purity calcium carbonate is shown as CaCO₃-a, pseudoboehmite alumina as Al₂O₃-a and ultrafine powder alumina binder asBinder I. The reactive agents were prepared by adding Binder I in a massratio of 0.05 or Binder II in a mass ratio of 0.1, assuming that themass after the alumina and the alkaline earth metal compound wereblended is 1.0. The decomposition test was performed using the reactiveagents shown in Test Condition 1 of Tables 2 to 6 based on TestCondition 2. The results are shown by the decomposition ratio offluorine compounds every hour after the gas to be treated was introducedand by the concentration (vol %) of CO or F ion present in the gastreated.

Decomposition ratio=(concentration of fluorine compound in gas to betreated−concentration of fluorine compound in treatedgas)÷(concentration of fluorine compound in gas to be treated)×100(%)

EXAMPLES 1 TO 3

Using the reactive agents which varied in the ratio of alumina andcalcium carbonate blended in the reactive agent as shown in Table 2,decomposition reactions of CF₄ were performed. The alumina used waspseudo boehmite alumina (hereinafter simply referred to as “Al₂O₃-a”)and the alkaline earth metal compound used was high-purity calciumcarbonate (hereinafter simply referred to as “CaCO₃-a”). The reactiontemperature was constantly 650° C. and the oxygen concentration was setto 3.5 vol %.

The results obtained are shown in Table 2. With any blending ratio, adecomposition ratio of 99% or more was attained within 3 hours after thegas to be treated was introduced. Furthermore, as shown in Table 2,almost no F ion or CO was detected in the treated gas of Example 1.

EXAMPLES 4 TO 6

A reactive agent prepared under the same conditions as in Example 2 wasused for decomposition reactions of CF₄ by varying the reactiontemperature. The results are shown in Table 2. At a reaction temperatureof 600° C., a decomposition ratio of 99% or more was attained and at700° C., a decomposition ratio of 99.9% or more was attained within 5hours after the gas to be treated was introduced.

EXAMPLE 7

A decomposition reaction of CF₄ was performed under the same conditionsas in Example 6 except that the temperature at the baking of reactiveagent was changed from 550° C. to 700° C. The results obtained are shownin Table 2. The CF₄ decomposing ratio was the same and 99% or more,however, the decomposition ratio was gradually decreased as comparedwith Example 6.

EXAMPLES 8 AND 9

Decomposition reactions of CF₄ were performed under the same conditionsas in Example 2 and Example 7 except that the alumina in the reactiveagent was changed to pseudo boehmite alumina baked at 550° C. for 3hours (hereinafter simply referred to as Al₂O₃-b). In Example 8, adecomposition reaction using a reactive agent having added theretoBinder II was also conducted. The results are shown in Table 2. Thedecomposition ratio of Example 8 was almost the same as in Example 2,revealing no difference due to variation of the binder. In Example 9,the test was performed by setting both the baking temperature and thereaction temperature at 700° C. in the same manner as in Example 7,then, a high decomposition ratio could be maintained.

TABLE 2 Test Condition 2 Test Condition 1 Baking Reactive Agent Temper-Reaction Kind (combination and blending ature Temper- and ratio ofmaterials) (° C.) ature Concen- Test Results Blending Amount (° C.)tration Decomposition Ratio of Fluorine Compound Ratio of Oxygen of Gasin Treated Gas after Aging (%), Composition (mass Reactive Concen-Fluorine Fluorine Ion Concentration in ( ) and CO (combination ratio ofAgent tration Compound Concentration in [ ], (vol %) Example ofmaterials) materials) Binder (ml) (vol %) (vol %) 1 Hr 2 Hr 3 Hr 4 Hr 5Hr 1 Al₂O₃-a/CaCO₃-a 0.19/0.81 I 550 650 CF₄ 3.0 >99.9 >99.9 99.9 99.195.9 35 3.5 [<0.001] [<0.001] [<0.001] [<0.001] (<0.0001) 2Al₂O₃-a/CaCO₃-a 0.30/0.70 I >99.9 >99.9 >99.9 99.7 97.6 3Al₂O₃-a/CaCO₃-a 0.45/0.55 I >99.9 >99.9 >99.9 98.8 60.4 4Al₂O₃-a/CaCO₃-a 0.30/0.70 550 550 CF₄ 3.0 82.2 82.0 81.3 78.0 68.0 353.5 5 Al₂O₃-a/CaCO₃-a 0.30/0.70 I 550 600 99.8 99.7 98.8 94.7 89.1 353.5 6 Al₂O₃-a/CaCO₃-a 0.30/0.70 I 550 700 >99.9 >99.9 >99.9 >99.9 99.935 3.5 7 Al₂O₃-a/CaCO₃-a 0.30/0.70 I 700 700 CF₄ 3.0 >99.9 >99.9 99.899.0 94.0 35 3.5 8 Al₂O₃-b/CaCO₃-a 0.30/0.70 I 550 650 CF₄3.0 >99.9 >99.9 >99.9 99.4 94.9 II 35 3.5 >99.9 >99.9 >99.9 99.5 94.6 9Al₂O₃-b/CaCO₃-a 0.30/0.70 I 700 700 >99.9 >99.9 >99.9 >99.9 99.6 35 3.5

EXAMPLES 10 TO 13

Decomposition reactions of CF₄ were performed under the same conditionsas in Example 2 and Example 6 except that the calcium carbonate in thereactive agent was changed to light calcium carbonate (hereinaftersimply referred to as “CaCO₃-b”) or heavy calcium carbonate (hereinaftersimply referred to as “CaCO₃-c”). The results obtained are shown inTable 3. It can be seen that the decomposition ratio of CF₄ correspondsto the total amount of impurities in each calcium carbonate shown inTable 1 and has a tendency to decrease in the order of CaCO₃-a (Examples2 and 6)>CaCO₃-b (Examples 10 and 11)>CaCO₃-c (Examples 12 and 13).

EXAMPLES 14 TO 16

Decomposition reactions of CF₄ were performed under the same conditionsas in Example 13 except that the alumina in the reactive agent waschanged to the alumina (Al₂O₃-b, Al₂O₃-c or Al₂O₃-d) shown in Table 1.The results obtained are shown in Table 3. It is seen that thedecomposition ratio of CF₄ corresponds to the amount of impurities ineach Al₂O₃ and decreases in the order of Al₂O₃-a (Example 13)≧Al₂O₃-b(Example 14)>Al₂O₃-c (Example 15)>Al₂O₃-d (Example 16).

EXAMPLE 17

A decomposition reaction was performed under the same conditions as inExample 1 except that the fluorine compound was changed from CF₄ toC₂F₆. The results obtained are shown in Table 3. The decomposition ratioof C₂F₆ reached 80% or more within 3 hours after the gas to be treatedwas introduced.

EXAMPLES 18 TO 20

Decomposition reactions of C₂F₆ were performed under the same conditionsas in Example 2 except that the reaction temperature and the oxygenconcentration were changed. The results obtained are shown in Table 3.In Example 18, the reaction temperature and the oxygen concentrationwere set to 600° C. and 3.5 vol %, respectively, however, thedecomposition ratio of C₂F₆ was on the same level as in Example 17 andthe effect of controlling the generation of CO was not sufficientlyhigh.

In Examples 19 and 20, the decomposition reaction was performed bychanging the reaction temperature to 650° C. and the oxygen gasconcentration to 0 vol % or 20 vol %. In either example, thedecomposition ratio of C₂F₆ reached 90% or more within 3 hours after thegas to be treated was introduced. In Example 19, nearly 3% of CO wasgenerated, whereas in Example 20, CO was not detected until 3 hoursafter the gas to be treated was introduced. From this, it is seen thatgeneration of CO can be almost completely controlled by allowing oxygengas to be present.

TABLE 3 Test Condition 2 Test Condition 1 Baking Reactive Agent Temper-Reaction Kind (combination and blending ature Temper- and ratio ofmaterials) (° C.) ature Concen- Test Results Blending Amount (° C.)tration Decomposition Ratio of Fluorine Compound Ratio of Oxygen of Gasin Treated Gas after Aging (%), Composition (mass Reactive Concen-Fluorine Fluorine Ion Concentration in ( ) and CO (combination ratio ofAgent tration Compound Concentration in [ ], (vol %) Example ofmaterials) materials) Binder (ml) (vol %) (vol %) 1 Hr 2 Hr 3 Hr 4 Hr 5Hr 10 Al₂O₃-a/CaCO₃-b 0.30/0.70 I 550 650 CF₄ 3.0 >99.9 >99.9 99.5 99.098.5 35 3.5 11 Al₂O₃-a/CaCO₃-b 0.30/0.70 I 700 >99.9 >99.9 >99.9 99.694.9 3.5 12 Al₂O₃-a/CaCO₃-c 0.30/0.70 I 550 650 CF₄ 3.0 >99.9 99.9 98.894.7 — 35 3.5 13 Al₂O₃-a/CaCO₃-c 0.30/0.70 I 700 >99.9 >99.9 >99.9 99.9— 3.5 14 Al₂O₃-b/CaCO₃-c 0.30/0.70 I 550 700 CF₄ 3.0 >99.9 >99.9 99.999.4 — 15 Al₂O₃-c/CaCO₃-c 0.30/0.70 35 3.5 >99.9 99.7 97.8 89.4 — 16Al₂O₃-d/CaCO₃-c 0.30/0.70 32.9 27.4 — — — 17 Al₂O₃-a/CaCO₃-a 0.19/0.81 I550 650 C₂F₆ 3.0 85.8 84.9 82.8 75.2 62.5 35 3.5 [0.021] [0.020] [0.020][0.088] [0.182] 18 Al₂O₃-a/CaCO₃-a 0.30/0.70 600 86.5 84.9 81.2 70.249.7 3.5 [0.14] [0.13] [0.52] [0.60] [0.47] 19 Al₂O₃-a/CaCO₃-a 0.30/0.70I 550 650 C₂F₆ 3.0 98.3 97.4 89.2 73.3 45.7 35 0 [2.77] [2.74] [3.16][2.04] [1.32] 20 Al₂O₃-a/CaCO₃-a 0.30/0.70 I 650 99.2 97.4 91.3 72.235.5 20.0 [<0.001] [<0.001] [<0.001] [0.006] [0.080]

EXAMPLES 21 TO 24

Decomposition reactions of C₂F₆ were performed under the same conditionsas in Example 20 except that the reactive agent used was obtained byadding a metal oxide (Example 21: V₂O₅, Example 22: SnO₂, Example 23:CuOO+SnO₂, Example 24: Cr₂O₃) to a reactive agent having a mass ratio ofAl₂O₃-a/CaCO₃-a=0.3/0.7 and the oxygen concentration was changed from 20vol % to 3.5 vol %. The results obtained are shown in Table 4. Thedecomposition ratio of C₂F₆ was almost the same as the results inExamples 18 to 20, but CO was scarcely detected even with an oxygen gasconcentration of 3.5 vol % was present. From this, it is seen that byadding a metal oxide to the reactive agent, CO can be almost completelyoxidized even under a low oxygen partial pressure.

EXAMPLES 25 AND 26

Decomposition reactions of a mixed gas of CF₄ and C₂F₆ were performedunder the same conditions as in Example 2 except that two units ofreaction tubes were connected (reactive agent 35×2=70 ml) and thereaction temperature was changed to 550° C. or 650° C. The resultsobtained are shown in Table 4. In Example 25 where the reactiontemperature was 550° C., the decomposition ratio of C₂F₆ was as low asabout 70% but the decomposition ratios of both C₂F₆ and CF₄ were almostconstantly maintained. In Example 26 where the reaction temperature was650° C., a high decomposition ratio could be maintained for both CF₄ andC₂F₆.

EXAMPLES 27 AND 28

Decomposition reactions of CF₄ were performed under the same conditionsas in Example 2 except that CO was present together or HF and SiF₄ werepresent together. The results obtained are shown in Table 4. In Example27 where CO was present together, CO was not detected in the treatedgas, and in Example 28 where HF and SiF₄ were present together, F ionwas not detected in the treated gas.

EXAMPLES 29 TO 39

Decomposition reactions were performed under the same conditions as inExample 2 by varying the kind and the concentration of the fluorinecompound and the reaction temperature. The results are shown in Table 5.Despite different reaction temperatures, a high decomposition ratio wasattained for any fluorine compound. The structures of fluorine compoundsused in Examples 31 to 39 are shown below.

EXAMPLE 40

A decomposition reaction of CF₄ was performed under the same conditionsas in Example 2 except that CaCO₃ in the reactive agent was changed toSrCO₃. The results obtained are shown in Table 5. Although thedecomposition ratio slightly decreases in the case of SrCO₃, thereactive agent can be used as a reactive agent for decomposing fluorinecompounds.

COMPARATIVE EXAMPLES 1 AND 2

The tests were performed in the same manner as in the Examples withrespect to the preparation of the reactive agent, the reaction exampleand the like.

Decomposition reactions of CF₄ were performed under the test conditionsshown in Table 6 using a reactive agent comprising only alumina. As aresult, the reaction ratio was abruptly reduced 2 hours after the gas tobe treated was introduced.

COMPARATIVE EXAMPLES 3 AND 4

Reactive agents were prepared under the same conditions as in Example 2except that MnO₂ or Fe₂O₃ was used in place of CaCO₃ in the reactiveagent and the decomposition reaction of CF₄ was performed at 700° C. Theresults obtained are shown in Table 6. In either example, thedecomposition ratio was low from the beginning.

TABLE 4 Test Condition 2 Test Condition 1 Baking Reactive Agent Temper-Reaction Kind (combination and blending ature Temper- and ratio ofmaterials) (° C.) ature Concen- Test Results Blending Amount (° C.)tration Decomposition Ratio of Fluorine Compound Ratio of Oxygen of Gasin Treated Gas after Aging (%), Composition (mass Reactive Concen-Fluorine Fluorine Ion Concentration in ( ) and CO (combination ratio ofAgent tration Compound Concentration in [ ], (vol %) Example ofmaterials) materials) Binder (ml) (vol %) (vol %) 1 Hr 2 Hr 3 Hr 4 Hr 5Hr 21 V₂O₅ added to 0.97/0.03 I 550 650 C₂F₆ 3.0 99.0 97.4 90.3 72.335.0 Example 20 35 3.5 [<0.001] [<0.001] [0.001] [0.006] [0.010] 22 SnO₂added to 0.97/0.03 99.0 96.7 91.5 72.0 40.3 Example 20 [<0.001] [<0.001][<0.001] [0.024] [0.023] 23 CuO + SnO₂ 0.98/ I 98.9 97.3 91.2 73.2 36.3added to 0.005 + [<0.001] [<0.001] [<0.001] [<0.001] [<0.001] Example 200.015 24 Cr₂O₃ added to 0.97/0.03 I 98.7 97.0 90.1 72.7 38.6 Example 20[<0.001] [0.003] [0.027] [0.047] [0.030] 25 Al₂O₃-a/CaCO₃-a 0.30/0.70 I550 550 CF₄ 1.5 99.7 99.7 99.7 99.5 99.4 35 × 2 3.5 C₂F₆ 1.5 68.9 68.968.9 62.9 62.8 26 Al₂O₃-a/CaCO₃-a 0.30/0.70 I 650 CF₄1.5 >99.9 >99.9 >99.9 >99.9 >99.9 3.5 C₂F₆ 1.5 >99.9 >99.9 >99.9 99.899.8 27 Al₂O₃-a/CaCO₃-a 0.30/0.70 I 550 650 CF₄ 3.0 >99.9 >99.9 >99.999.8 90.2 35 3.5 CO 0.5 [<0.001] [<0.001] [<0.001] [<0.001] [<0.001] 28Al₂O₃-a/CaCO₃-a 0.30/0.70 I CF₄ 0.5 >99.9 >99.9 >99.9 >99.9 >99.9 HF 0.5(<0.0001) (<0.0001) (<0.0001) (<0.0001) (<0.0001) SiF₄ 0.5

TABLE 5 Test Condition 2 Test Condition 1 Baking Reactive Agent Temper-Reaction (combination and blending ature Temper- ratio of materials) (°C.) ature Test Results Blending Amount (° C.) Kind and DecompositionRatio of Fluorine Compound Ratio of Oxygen Concentration Gas in TreatedGas after Aging (%), Composition (mass Reactive Concen- of FluorineFluorine Ion Concentration in ( ) and CO (combination ratio of Agenttration Compound Concentration in [ ], (vol %) Example of materials)materials) Binder (ml) (vol %) (vol %) 1 Hr 2 Hr 3 Hr 4 Hr 5 Hr 29Al₂O₃-a/CaCO₃-a 0.30/0.70 I 550 200 CHClF₂0.5 >99.9 >99.9 >99.9 >99.9 >99.9 35 3.5 30 Al₂O₃-a/CaCO₃-a 0.30/0.70 I350 CHF₃ 0.5 >99.9 >99.9 >99.9 >99.9 >99.9 3.5 31 Al₂O₃-a/CaCO₃-a0.30/0.70 I 200 C₂F₄ 0.5 >99.9 >99.9 >99.9 >99.9 >99.9 3.5 32Al₂O₃-a/CaCO₃-a 0.30/0.70 I 300 C₂HClF₄0.5 >99.9 >99.9 >99.9 >99.9 >99.9 3.5 33 Al₂O₃-a/CaCO₃-a 0.30/0.70 I 500C₂Cl₂F₄ 0.5 >99.9 >99.9 >99.9 >99.9 >99.9 34 Al₂O₃-a/CaCO₃-a 0.30/0.70 I3.5 C₂H₂F₄ 0.5 >99.9 >99.9 >99.9 >99.9 >99.9 35 Al₂O₃-a/CaCO₃-a0.30/0.70 I 200 C₃HF₇O 0.5 >99.9 >99.9 >99.9 >99.9 >99.9 36Al₂O₃-a/CaCO₃-a 0.30/0.70 I 3.5 C₃F₇O 0.5 >99.9 >99.9 >99.9 >99.9 >99.937 Al₂O₃-a/CaCO₃-a 0.30/0.70 I 600 C₄F₈0.5 >99.9 >99.9 >99.9 >99.9 >99.9 3.5 38 Al₂O₃-a/CaCO₃-a 0.30/0.70 I 500C₅F₈ 0.5 >99.9 >99.9 >99.9 >99.9 >99.9 3.5 39 Al₂O₃-a/CaCO₃-a 0.30/0.70I 600 SF₆ 0.5 >99.9 >99.9 >99.9 >99.9 >99.9 3.5 40 Al₂O₃-a/CaCO₃-a0.30/0.70 I 650 CF₄ 3.0 96.0 94.3 91.3 76.5 65.5 3.5

TABLE 6 Test Condition 1 Test Condition 2 Reactive Agent Baking(combination and blending Temper- Reaction Kind ratio of materials)ature Temper- and Blending (° C.) ature Concen- Test Results RatioAmount (° C.) tration Decomposition Ratio of Fluorine Compound (mass ofOxygen of Gas in Treated Gas after Aging (%), Compara- Composition ratioof Reactive Concen- Fluorine Fluorine Ion Concentration in ( ) and COtive (combination respective Agent tration Compound Concentration in [], (vol %) Example of materials) materials) Binder (ml) (vol %) (vol %)1 Hr 2 Hr 3 Hr 4 Hr 5 Hr 1 Al₂O₃-a 1.0 I 550 650 CF₄ 3.0 >99.9 19.7 — —— 35 3.5 [<0.001] [<0.001] — — — 2 Al₂O₃-b 1.0 I 700 750 CF₄ 3.0 >99.947.8 40.8 38.3 — 35 0 [<0.005] [0.003] [<0.001] — — 3 Al₂O₃-a/MnO₂0.30/0.70 I 550 700 CF₄ 3.0 8.5 3.0 — — — 35 3.5 4 Al₂O₃-a/Fe₂O₃0.30/0.70 I 550 700 CF₄ 3.0 43.4 32.3 — — — 35 3.5

EXAMPLE 41

A silicon oxide film was etched using an etching gas comprising 20 sccmof CF₄, 20 sccm of CHF₃ and 400 sccm of argon gas. A part of the gasdischarged from this dry etching step was introduced using a nitrogencarrier gas into an apparatus shown in FIG. 1 filled with the samereactive agent as in Example 23. A gas at the outlet of thedecomposition apparatus was sampled 3 hours after the initiation of thedecomposition test and analyzed by gas chromatography. As a result, theconcentrations of CF₄ and CHF₃ both were 10 vol ppm or less and the COconcentration was also 10 vol ppm or less. The fluorine ionconcentration was analyzed by water extraction ion chromatography andthen found to be 1 vol ppm or less.

As described herein, when the reactive agent of the present invention isused, fluorine compounds can be efficiently decomposed at a relativelylow temperature by a simple formulation and the fluorine generated upondecomposition can be fixed as a harmless substance. In other words, thepresent invention can be implemented using a simple decompositionapparatus by a simple treatment operation. The decomposition efficiencyis high and when oxygen is allowed to be present together, thegeneration of carbon monoxide can also be controlled. Moreover, thedecomposition product becomes a stable alkaline earth metal fluoridesuch as CaF₂, therefore, the after-treatment is easy. Also, the effecton the reduction in costs for the reactive agent is by far higher. Inparticular, the present invention can greatly contribute to thedecomposition of used fluorine compounds generated in the manufacturingprocess of semiconductor devices.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

What is claimed is:
 1. A reactive agent for decomposing fluorinecompounds, consisting essentially of alumina, a carbonate of magnesium,calcium, strontium or barium, and at least one oxide of a metal selectedfrom the group consisting of copper and tin, wherein the carbonate andoxide are in powder form.
 2. The reactive agent for decomposing fluorinecompounds as claimed in claim 1, wherein said alumina has a specificsurface area of 50 m²/g or more.
 3. The reactive agent for decomposingfluorine compounds as claimed in claim 1 or 2, wherein said alumina ispseudo boehmite alumina.
 4. The reactive agent for decomposing fluorinecompounds as claimed in claim 1 or 2, wherein said alumina is obtainedby baking pseudo boehmite alumina at a baking temperature of from 400 to1,000° C.
 5. The reactive agent for decomposing fluorine compounds asclaimed in claim 1 or 2, wherein the alumina and the carbonate presentin said reactive agent each is in the form of powder having a particlesize of 100 μm or less.
 6. The reactive agent for decomposing fluorinecompounds as claimed in claim 1 or 2, wherein the alumina and thecarbonate are present in said reactive agent at a mass ratio of from 1:9to 1:1.
 7. The reactive agent for decomposing fluorine compounds asclaimed in claim 1 or 2, wherein the content of said metal oxide is from1:99 to 5:95 in terms of a ratio to the total mass of said alumina andsaid carbonate of magnesium, calcium, strontium or barium.
 8. Thereactive agent for decomposing fluorine compounds as claimed in claim 1or 2, which has an alkali metal content of 0.1 mass % or less.
 9. Thereactive agent for decomposing fluorine compounds as claimed in claim 1or 2, which is a granular product obtained by baking at a temperature offrom 400 to 700° C.
 10. The reactive agent for decomposing fluorinecompounds as claimed in claim 9, which is a granular product having aparticle size of from 0.5 to 10 mm.
 11. The reactive agent fordecomposing fluorine compounds as claimed in claim 1 or 2, which has awater content of 1 mass % or less.
 12. The reactive agent fordecomposing fluorine compounds as claimed in claim 1, wherein saidcarbonate is calcium carbonate.